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Topics in X-ray astronomy - Tuebingen February 2004 S.Mereghetti Spin Period (s) Maximum X-ray Luminosity (erg/s) Most accreting pulsars are in massive binaries AXP are only found in the narrow period range 5-12 s AXP in the context: Accreting pulsars

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Topics in X-ray astronomy - Tuebingen February 2004 S.Mereghetti No evidence for massive companion stars limits on a x sin i from timing limits on F x /F opt from optical/IR observations Period of a few seconds (6-12 s) Almost steady spin down Very soft X-ray spectrum kT BB 3-4 AXP PROPERTIES

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Topics in X-ray astronomy - Tuebingen February 2004 S.Mereghetti a spinning down pulsar, with a soft X-ray spectrum, apparently not powered by accretion from a (massive) companion star, and with luminosity larger than the rotational energy loss (assuming a neutron star) Operational definition of AXP

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Topics in X-ray astronomy - Tuebingen February 2004 S.Mereghetti Magnetar model (Thompson and Duncan) Emission powered by magnetic field decay and/or enhanced cooling Originally developed for SGRs where evidence for high B is stronger due to large flares and bursts Extended to AXP due to similar P and dP/dt values Isolated NS with B > 10 14 Gauss

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Topics in X-ray astronomy - Tuebingen February 2004 S.Mereghetti AXP=SGR ? Only observational selection effects introduced a distinction between these sources belonging to the same class of objects: in AXP the quiescent, pulsating emission was discovered first SGR were discovered through their bursts

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Topics in X-ray astronomy - Tuebingen February 2004 S.Mereghetti Despite the large flux variation the spectral shape did not vary BB+PL in both observations kT = 0.6 keV phot. Index = 3... these are the typical parameters seen in this source

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Topics in X-ray astronomy - Tuebingen February 2004 S.Mereghetti SGR1806-20 entered a new period of activity in July 2003 An INTEGRAL ToO observation started on 3 September 2003, while the source was still active INTEGRAL continued to observe SGR 1806-20 (l = 9.99 deg, b = -0.24 deg) during the Galactic Center Deep Exposre (GCDE) until mid October 24 bursts were detected by IBIS in real time by the INTEGRAL Burst Alert System (IBAS) and confirmed later by off-line analysis

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Topics in X-ray astronomy - Tuebingen February 2004 S.Mereghetti 24 bursts from SGR 1806-20 have been detected with the INTEGRAL Burst Alert System. ToO GCDE INTEGRAL Julian Day Number of bursts/day

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Topics in X-ray astronomy - Tuebingen February 2004 S.Mereghetti THE SGR BURSTS OBSERVED BY IBIS ARE NORMAL IN MOST RESPECTS Durations, energy spectra are typical However, the fluences are very low,~1.5x10 - 8 erg/cm 2, 25-100 keV These are the among the weakest bursts seen from this SGR; thanks to imaging, we are certain that the source is indeed SGR1806-20

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Topics in X-ray astronomy - Tuebingen February 2004 S.Mereghetti Conclusions 1) XMM / EPIC detected the first significant variation in the flux and pulsed fraction of the AXP 1048 the spectral invariance is a further evidence that the PL+BB spectral decomposition does not have a physical meaning 2) INTEGRAL / IBIS detected the first evidence for spectral evolution of fain SGR bursts as well as a hardness intensity anticorrelation these properties are not (yet) foreseen in the magnetar model